1. Field of the Invention
The present invention relates to an improvement of an information recording/reproducing-apparatus such as a video tape recorder (VTR) and a digital audio tape recorder (DAT) for recording and reproducing information signals such as a video signal and an audio signal on and from a recording medium, and an information recording/reproducing method applied to the apparatus.
2. Description of the Related Art
FIG. 1 is a schematic plan view showing tracks (TR1-TR14) formed on a magnetic tape by a digital video tape recorder for recording digitized video and audio information thereon in a helical scanning system.
In a digital video tape recorder (referred to as digital VTR) employing a helical scanning system, a magnetic tape is helically wound around a rotary drum having magnetic heads, and video and audio information signals being digtized are recorded on the magnetic tape.
As shown in FIG. 1, in this example, the audio information signals of two channels (CH1, CH2) and the video information signal are recorded in a time sharing manner on each of tracks formed on a magnetic tape T.
Video information signal of one video frame period included in nth frame is recorded on tracks TR2 to TR7, and the same included in the subsequent (n+1)th frame is recorded on tracks TR8 to TR13.
During the one video frame period of the nth frame, the audio information signal of CH1 is recorded on the track TR2 to TR4 and the audio information signal of the CH2 is recorded on the track TR5 to TR7. In this example, an amount of the audio information signal to be recorded during the one video frame period is made constant.
Generally, in order to renew the information recorded on a part of the tracks, the part of the track is preliminarily erased by a flying erase head. Then, new information signal is recorded on the erased part by a magnetic head. For instance, when the video information signals of the nth and (n+1)th frames are renewed, the video signals of the tracks TR2 to TR13 are erased, and new video signals are recorded thereon. The reason of the preliminary erasure by using the flying erase head is to prevent an error rate at reproduction from increasing, otherwise an overwriting without such a preliminary erasure causes a large error rate at reproduction of the new information signal.
Taking account of tracking error between the former recording and the renewing of the information, it is desirable to use a flying erase head having a track width larger than that of the track. However, this flying erase head causes a problem to erase parts of the tracks TR1 and TR14 in a track width direction, which should not be erased, resulting in an increase of the error rate because of a decrease of a signal level at reproduction. When the error rate developed exceeds a limit of error correcting ability of the apparatus, the reproduced image is degraded in quality due to a partial loss of the information data.
Generally, to prevent a part of a track from being undesirably erased, non-recorded sections, so called guard bands, are provided between the tracks. Thereby, it is possible to prevent the undesirable erasure of the tracks, however, these guard bands cause a problem to increase a track pitch between the tracks, resulting in a decrease of recording capability of the magnetic tape of a given length.
FIG. 2 is a schematic plan view showing a track pattern having guard bands at every two tracks in the prior art.
As a countermeasure to avoid such an over-erasure, guard bands are provided between groups of two tracks as shown in FIG. 2. Thereby, it is possible to prevent the partial track erasure without decreasing much recording capacity upon renewal of recorded information as a unit of frame, and to prevent the increase of the error rate upon reproduction.
However, when one of the two channels of the audio information signals is desired to be rewritten, there occurs a problem as follows.
Specifically, when the audio information signal of CH1 recorded in the nth frame and the (n+1)th frame is desired to be rewritten, parts of the audio data of CH2 recorded on the tracks TR5 and TR11 are erased in the track width direction because the guard bands are provided between the tracks TR1, TR2 and between the tracks TR7, TR8, but not between the tracks TR4, TR5 and between the tracks TR10, TR11.